On a summer night, at a sawmill in the mountains, two teenagers witness a quadruple murder. Wanting to hide their gay relationship, Yann and Lucas decide to remain silent. Hélène Siquelande, a former member of the National Guard that left to focus on her family, now is entrusted with the investigation. Hélène is also the foster mother of one of the teenagers, Yann. The boys' lie causes a chain reaction, and now the killer is looking for them.

In Perpignan, the killer explodes a bomb in the city center. The nightclub targeted belongs to Milo Ubieta. He is the father of a runaway teenager, Lena. The apartment in which he had locked her shattered and she managed to flee to find a certain "Lancelot". Hélène Siquelande tries to find a link between that and the killing at the sawmill because she does not believe in coincidences.

"Lancelot" is the killer of the sawmill. Lena, the teenager who slept with him, is found dead. Yann and Lucas are in a panic since they received photos of their secret encounter, taken in the night of the slaughter. Is the killer playing with them? If Yann is afraid for his life, Lucas is terrified of being outed. The media is beginning to cover this case and the political pressure is accentuating over Hélène. She is surprised to have many crimes to solve with so few clues.